Lead in the form of Pb.sub.3 O.sub.4, known as "red lead," has been widely used in rust-inhibiting paints and primers for iron and steel. Other lead compounds have also been important in paint pigments. Lead chromate, PbCrO.sub.4, is a brilliant yellow and is used in road markings. A mixture of PbCO.sub.3 and Pb(OH).sub.2, is the traditional formulation of the pigment used in white paint. In the last twenty years, lead-based pigments for use in household paints have been abandoned. Lead is a toxic heavy metal and the sweet flavor which it can impart to paints has been the cause of incidents of lead poisoning among small children who eat paint flakes. Due to a heightened awareness of the danger of the release of heavy metals into the environment, the abandonment of lead pigment from structures such as bridges, watertowers and heavy machinery has also resulted. The massive historic use of lead-containing paints on these same structures has lead to considerable costs and difficulty in their maintenance. Bridges watertowers, heavy equipment and the like, must periodically be stripped of their paint coating and repainted. This stripping of lead-based paints can result in releasing considerable amounts of lead into the environment.
Safe elimination of these hazardous materials is gaining more attention due to the new Environmental Protection Agency (EPA) laws imposed because of the extreme toxicity of many of the resulting lead waste products. Wastes from lead paint removal are often hazardous due not only to the high lead content but also from the presence of zinc, cadmium, copper, nickel, barium and other heavy metals present. Handling and disposal of these hazardous wastes is far more complicated and expensive than if they were nonhazardous.
A key element of the EPA regulatory scheme for protecting the environment from heavy metal toxins is determining when regulations apply. A material such as lead paint is not a toxic waste when it is fulfilling its intended purpose as a protective coating on a bridge or structure. Hence, there is a regulatory and logical distinction between toxic materials and toxic wastes. The distinction is that many toxic materials perform useful and even essential functions in our society and it is only the improper disposal thereof that causes harm to the environment. However, once a toxic waste is generated by sandblasting a bridge to remove lead paint for example, the sandblasting operation is considered to generate a toxic waste material which falls under the governing EPA regulations. Thus, it is extremely beneficial if the lead paint is rendered nonhazardous prior to its removal from the surface. This eliminates the production of hazardous wastes thereby avoiding the requirement of adhering to strict EPA regulations since no hazardous wastes are ever produced. This reduces costs greatly and simplifies the methods of handling and disposal of the resulting nonhazardous waste.
The EPA laws and regulations recognize the distinction between lead which is soluble and, therefore, hazardous and lead which is not soluble and, therefore, nonhazardous. This recognition comes about in terms of tests which define the toxicity of the material by the amount of lead which can be leached from a waste sample under standard test conditions. Environmental regulations which have been drawn up to deal with heightened awareness of lead as a source of toxicity in the environment has divided all materials into two classes, toxic and nontoxic wastes. Toxic wastes are defined by a standard test which determines the leachability of a toxin such as lead. The most common test which is used by the EPA is the Toxicity Characteristic Leaching Procedure (TCLP) which measures the amount of leaching of various hazardous contaminants from a solid waste.
The chemistry involved behind rendering leaded paint nonhazardous is controlled both by the pH as well as by forming insoluble compounds with the lead. Any chemical compound or element which achieves those goals can be used, however, a compound containing phosphorus and a pH buffer may sufficiently bind the lead and cause a favorable pH condition, thereby immobilizing it.
U.S. Pat. No. 5,637,355 entitled "Method of Nonhazardous Removal of Paint Containing Heavy Metals and Coating Preparation for Same" by Robert Stanforth and Paul Knopp outlining this technology is herein incorporated by reference.
Current techniques to avoid EPA regulation by eliminating generation of a hazardous waste include adding lead-reactive treatment chemicals directly to the blasting media. As the lead paint is removed by blasting, it is mixed with the treatment chemicals present in the blasting media. Due to the fact that the treatment chemical is directly added to the grit of blasting media (e.g. sand or zircon) and preblended, and subsequently blasted on the steel surfaces of bridges, watertowers, etc., production of hazardous wastes is avoided. Typically, the lead-reactive chemical is a cement-type compound. This method has several drawbacks. First, this method produces excessive dusting resulting in personnel safety hazards, reduced visibility and breathing control problems for workers. Additionally, the cement treatment additives to the grit must be in a fairly high dose of approximately 20%. The cement treatment chemical is not a good cutting medium (not as good as the zircon or sand grit) and, therefore, the cutting efficiency of the blasting is reduced by 20%, resulting in the lead paint removal taking 20% longer.
Another method of rendering the lead paint nonhazardous is via a treatment process which introduces an additive which renders heavy metals nonhazardous to a coating preparation formula. This coating preparation is then applied over an existing lead paint before the lead paint is removed from the surface. The lead paint is thereby rendered nonhazardous before it is removed from its surface and becomes a waste material. A problem associated with this method is that there are no coating preparations currently available which would sufficiently carry the lead-reactive compound and have properties to facilitate proper treatment.
The key to the present invention is producing an adequate carrier for the lead-reactive additives. In the present invention, this carrier for the lead-reactive additive is a paint formulation. This paint must contain a sufficient quantity of the lead treatment additives which will immobilize the lead contained in the paint. It is also important that the carrier be able to hold substantial amounts of the lead reactive additives without having to be repeatedly applied or result in extremely thick layers of carrier to the lead-painted surface. Also, it would be advantageous if the carrier paint holds the lead treatment additives uniformly throughout thereby enabling the entire leaded surface to be treated in a consistent manner. In addition, it would be advantageous if the carrier paint could be removed by a number of different lead-paint removal systems such as sandblasting and other hard grit methods as well as soft grit methods utilizing water, plastic or even simple mechanical wire brush means. The TCLP test requires that the waste materials be water-soluble and, therefore, the carrier paint should be water-soluble for sufficient TCLP testing. The carrier paint should be able to cover and be subsequently removed from a myriad of different surfaces including steel, wood surfaces, gypsum, dry wall and plaster boards. The carrier paint must have the ability to coat leaded surfaces using conventional means ranging from an airless spray gun to a roller or brush and yet properly cover the lead-painted item with adequate thickness and consistency.
A problem encountered with simply utilizing off-the-shelf paints as the carrier is that off-the-shelf formulas do not provide some or all of the aforementioned characteristics for a number of reasons.